[Math] expected number of cards drawn when a card is chosen from a 52 deck and game ends on picking a heart

probability

I need help going about solving this problem:

Suppose a card game is played using a standard 52 card deck. Drawing a heart ends the game. Drawing anything other than a heart continues the game. There is no replacement of the drawn card back into the deck.

What is the expected number of cards drawn before the game ends (i.e when a heart is chosen)?

Best Answer

For the 39 non-hearts, define $A_i,\, 1\leq i\leq 39 $ to be the event that card $i$ appears before all the hearts. The number of draws until we get the first heart is $X=1+\sum_{i=1}^{39} 1_{A_i}$, and since $\mathbb{P}(A_i)=1/14$ we get $$\mbox{average number of draws} =\mathbb{E}(X)=1+\sum_i \mathbb{P}(A_i)=53/14\approx 3.79.$$